1. Field of the Invention
This invention relates to a class of devices which oscillate in response to a moving fluid to extract useful energy.
2. Prior Art
Windmills are the most commonly known devices utilizing the motion of a fluid, in that case air, to cause a rotary motion of the device in the production of useful energy. In the prior art, it is apparent that fixed site, horizontal or vertical axis windmills have received most consideration. The design of such steady state windmills tends to lead to complex and expensive structures, difficult to build and maintain. The regime of use, with relatively high centrifugal forces, requiring transmission of motions, gearboxes and rotational speed controls are contributing factors in the generally unsatisfactory economics of scale of these devices. The mass produced Hallady-Perry windmill of the 1920's and 1930's, once a common sight in rural areas has, today, been replaced by almost total electrification. The prior art is replete with devices which attempt to improve the efficiency and reduce costs of such windmill designs.
Today, with an increased public awareness of energy problems, experiments in alternative forms of energy generation have renewed interest in windmills. However, proposed devices, typified by interest on the part of NASA, Newsweek, Mar. 29, 1974, interview with R. D. Ginter in "Business & Finance," return to rotary windmill types.
In a more generalized sense, it is apparent that a variety of alternatives exist for the use of fluid motion in the generation of useful energy. Devices may be catagorized by the type of motion utilized, rotary in the case of the conventional windmill, linear in the case of a sailboat or oscillatory in the case of the invention described herein. Additionally, the type of mounting, fixed structurally or self-erecting provides functional breakdown in which to accurately classify these devices. While not strictly a windmill, the sailboat is a well known type of wind utilizing device by which to demonstrate the classification. Sailboats involve the generation of linear motion, movement of the vessel, and the wind responsive devices may be either structurally mounted with sails on masts and standing rigging or self-erecting in the case of spinnakers which tend to be restained by wires or guys and hold themselves in place in response to aerodynamic forces generated by the interaction of sail shape and the relative wind. The wide variety of possible devices existing within such a matrix reveals that many configurations are simpler than conventional rotary motion structurally mounted windmills and some extract more energy per unit weight. Additionaly, there are dynamic constraints on windmill efficiency. Generally, the physics of fluid flow, for a variety of well known reasons limits the magnitude of the force coefficient developed parallel to or normal to the relative fluid direction. This force coefficient is the lift coefficient for horizontal axis windmills and the drag coefficient differential for some vertical axis designs. Although the efficiency of the system increases with increases in force coefficient, the limiting range is in the order of 2.0 or less. These limiting factors, expense, size and dynamic efficiency have stimulated interest in the third type of fluid responsive device, the oscillatory system.